In order to prevent a timing chain from slipping on a drive sprocket fixed onto a crank shaft of an internal combustion engine, JPH10-246297A, published by Japan Patent Office in 1998, discloses a timing chain drive device provided with a slippage prevention rail.
The timing chain is looped around the drive sprocket, a driven sprocket fixed onto a cam shaft for an intake valve, and a driven sprocket fixed onto a cam shaft for an exhaust valve.
The slippage prevention rail is disposed in a position on the outside of an engaging part between the timing chain and the drive sprocket so as to prevent the timing chain from displacing radially outward.
The sprockets and the timing chain are disposed on the outside of a cylinder block and a cylinder head of the internal combustion engine, and enclosed in a chain case fitted to the cylinder block.
The timing chain drive device comprises a tension rail on a downstream side of the drive sprocket with respect to the travel direction of the timing chain. The tension rail is designed to provide the timing chain with a tensile force by pressing the timing chain inward as well as to guide the travel of the timing chain. The timing chain drive device also comprises a fixed guide located on the upstream side of the drive sprocket with respect to the travel direction of the timing chain for guiding the travel of the timing chain.
The slippage prevention rail is constructed to project toward the cylinder block from the chain case, and has a sufficient width to cover substantially the entire width of the timing chain. The slippage prevention rail prevents lubricant from scattering from the engaging part between the timing chain and the drive sprocket, and ensures a supply of lubricant to the friction surface between the tension rail and the timing chain, thereby preventing wear of the tension rail and extensional deformation of the timing chain.